The present invention relates to a chlorinated vinyl chloride resin composition for siding extrusion molding and a siding molded article using the same. More particularly, the present invention relates to a chlorinated vinyl chloride resin composition from which a siding molded article excellent in appearance, heat resistance, impact resistance and weatherability can be obtained, and a siding molded article obtained by using the same.
Vinyl chloride resins are excellent in processibility and mechanical properties and available at moderate prices. Therefore, those resins are used in a wide variety of fields including housing industry where the resin is processed into a molded article such as a window frame or a siding molded article such as a siding sheet.
Weatherability is required for siding molded articles since they are used outdoors for a long time. In view of this, siding molded articles are generally made to have a two-layered structure and the surface layer which is exposed to sunlight is made of a material having excellent weatherability to prevent discoloration and other harmful effects.
Such a two-layered structure molded article has a surface layer called xe2x80x9ccapstockxe2x80x9d and an inner layer called xe2x80x9csubstratexe2x80x9d. The composite can be prepared by a method such as coextrusion. A ratio of a thickness of the capstock to that of the substrate is usually about 25/75 to 10/90.
While materials other than a vinyl chloride resin having greatly improved discoloration resistance against weather are used for the capstock, a vinyl chloride resin is generally used for the substrate.
Furthermore, required properties other than weatherability are impact resistance in a temperature range at which a siding molded article is used, and heat resistance such that the molded article is hardly deformed when surface temperature is increased by sunlight. Since these properties greatly depend upon the substrate constituting major portion of a molded article, selection of a composition for the substrate becomes important.
A vinyl chloride resin generally used for the substrate does not have sufficient impact resistance only by compounding a lubricant or a stabilizer. However, it is known that desirable impact resistance can be obtained by compounding an impact resistance modifier such as a butadiene rubber or an acrylic rubber.
Furthermore, since heat deformation temperature of a vinyl chloride resin is in a range of about 60xc2x0 to 70xc2x0 C., such a vinyl chloride resin is suitable for the substrate of a light tone siding molded article whose surface temperature does not exceed 70xc2x0 C.
However, in the case of a siding molded article having dark color tone such as dark green, navy blue and brown, surface temperature thereof may reach at least 70xc2x0 C. For this reason, a vinyl chloride resin composition having relatively low heat resistance is not suitable for the substrate of the dark-color siding molded article.
On the other hand, a chlorinated vinyl chloride resin obtained by chlorinating a vinyl chloride resin is known as a relatively inexpensive, general-purpose resin and has the characteristic that heat deformation temperature thereof is higher by 20xc2x0 to 40xc2x0 C. than that of a vinyl chloride resin. With putting this property into good use, the chlorinated vinyl chloride resin is used for a hot-water pipe or a heat resistant plate for industrial use. It is predicted that a dark-color siding molded article having desired heat resistance can be obtained by using a chlorinated vinyl chloride resin for a siding molded article.
By the way, impact resistance at low temperature of a chlorinated vinyl chloride resin is smaller than that of a vinyl chloride resin. Therefore, when a chlorinated vinyl chloride resin is used as a substrate, it is difficult to obtain a siding molded article having desired impact resistance. Since a siding molded article is also used as an external wall of houses, it goes without saying that impact resistance at low temperature is required.
Furthermore, it is generally said that a chlorinated vinyl chloride resin is difficult to process since it has inferior heat stability and higher melt viscosity compared to those of a vinyl chloride resin. For example, when a chlorinated vinyl chloride resin composition is extrusion-molded, die pressure and extrusion torque for an extrusion molding machine may be raised. In addition, a molded article is colored and deteriorated in appearance, burn mark being generated during extrusion molding. Thus, desirable molded articles can not be obtained in some cases.
Other various resins have similar problems, which means that a resin has not been found yet, which has properties required for a dark-color siding molded article, that is, good appearance, excellent weatherability, heat resistance, impact resistance and processibility as well as economical efficiency.
The present invention was carried out in order to solve the above problems in prior arts. An object of the present invention is to provide a chlorinated vinyl chloride resin composition for siding extrusion molding which can provide a siding molded article having excellent processibility, good appearance, excellent heat resistance, impact resistance and weatherability, and to provide a siding molded article using the same.
Intense studies were conducted to solve the above problems. As a result, the present invention has been completed based on the findings that it is possible to obtain a chlorinated vinyl chloride resin composition for siding extrusion molding which can provide a siding molded article having excellent appearance, desirable weatherability, heat resistance and impact resistance without losing processibility by preparing a siding molded article using a particular chlorinated vinyl chloride resin composition.
That is, the present invention relates to a chlorinated vinyl chloride resin composition for siding extrusion molding, comprising 100 parts by weight of a chlorinated vinyl chloride resin and 3 to 20 parts by weight of an acrylic graft rubber copolymer, wherein the acrylic graft rubber copolymer contains 30 to 90% by weight of acrylic hollow rubber particles whose average void ratio is 3 to 90% by volume in a latex state.
It is preferable that the chlorinated vinyl chloride resin composition further comprises at least two tin stabilizers.
It is also preferable that the chlorinated vinyl chloride resin composition further comprises oxidation-type modified polyethylene wax having an acid number of 0.1 to 10 mg/g measured by JIS K 5902 as a lubricant.
In addition, it is preferable that the chlorinated vinyl chloride resin composition further comprises a dark-color pigment.
The present invention also relates to a siding molded article obtained by using the above chlorinated vinyl chloride resin composition for siding extrusion molding.
Preferably, the above siding molded article has Gardner strength of at least 0.68 mxc2x7kg/mm (1.5 inchxc2x7lbs/mil) at 23xc2x0 C. and HDT of at least 87.7xc2x0 C. (190xc2x0 F.).
The chlorinated vinyl chloride resin composition of the present invention comprises, as a base resin, a chlorinated vinyl chloride resin having excellent heat resistance, and an acrylic graft rubber copolymer containing 30 to 90% by weight of acrylic hollow rubber particles whose average void ratio is 3 to 90% by volume in a latex state, for improving weatherability and impact resistance of a molded article. If necessary, the chlorinated vinyl chloride resin composition of the present invention further comprises at least two kinds of tin stabilizers, at least one kind of oxidation-type modified polyethylene wax (lubricant) having an acid number of 0.1 to 10 mg/g measured by JIS K5902, and at least one kind of a dark-color pigment.
As described above, since a chlorinated vinyl chloride resin is used as a base resin, the composition has excellent heat resistance and may be also used for a substrate of a dark-color siding molded article. In addition, since an acrylic graft rubber copolymer containing 30 to 90% by weight of acrylic hollow rubber particles having a glass transition temperature (Tg) of at most 0xc2x0 C. and an average void ratio of 3 to 90% by volume in a latex state is used, impact resistance can be improved and a siding molded article having excellent weatherability can be obtained even when a siding molded article is prepared by using a chlorinated vinyl chloride resin as a base resin. In addition, when at least two tin stabilizers are used, heat stability at extrusion processing can be improved, and such a problem that burn mark is generated at extrusion molding is prevented. Further, when the above oxidation-type modified polyethylene wax is used, extrusion processibility can be improved by decreasing melt viscosity. When a dark-color pigment is used, it becomes possible to prepare dark-color molded articles whose use had been limited from the viewpoint of heat resistance, and a wider range of designs becomes available.
The above chlorinated vinyl chloride resin is prepared by chlorinating a vinyl chloride resin.
Examples of the vinyl chloride resin include a homopolymer of a vinyl chloride monomer, and a copolymer of a vinyl chloride monomer and a monomer copolymerizable therewith such as ethylene, propylene, vinyl acetate, vinyl chloride, allyl chloride, allyl glycidyl ether, acrylate ester or vinyl ether.
An average degree of polymerization of the vinyl chloride resin before chlorination is usually 500 to 1,300, preferably 500 to 1,200, more preferably 600 to 900 from the viewpoint of balance between mechanical strength and processibility.
As a method of chlorinating a vinyl chloride resin as a raw material, there are known a method of supplying chlorine to a vinyl chloride resin suspended in water to chlorinate the same by irradiation with a mercury lamp, a method of chlorination by heating, a method of chlorination in the presence of a catalyst such as a peroxide, a method of chlorination by irradiation with a mercury lamp in a chlorine gas stream, and the like.
The chlorinated vinyl chloride resin used in the present invention may be a resin obtained by any of these methods. The chlorination degree of the chlorinated vinyl chloride resin is usually 62 to 70% from the viewpoint of balance between heat resistance and melt viscosity.
Examples of the above chlorinated vinyl chloride resin include, but are not limited to, heat resistant Kanevinyl H727 (average polymerization degree: 700, chlorination degree: 67%, available from Kaneka Corporation), heat resistant Kanevinyl H827 (average polymerization degree: 700, chlorination degree: 68%, available from Kaneka Corporation), and the like. These may be used alone or in combination of two or more. Among them, heat resistant Kanevinyl H727 is preferable from the viewpoint of balance among heat resistance, processibility and mechanical properties.
In the present invention, the above acrylic graft rubber copolymer used together with the chlorinated vinyl chloride resin is an acrylic graft rubber copolymer containing 30 to 90% by weight of acrylic hollow rubber particles whose glass transition temperature(Tg) is at most 0xc2x0 C. and void ratio is 3 to 90% by volume in a latex state.
In order to improve weatherability, the above acrylic hollow rubber particles comprises 80 to 100% by weight, preferably 85 to 100% by weight of an acrylic monomer unit, and 0 to 20% by weight, preferably 0 to 15% by weight of a monomer unit copolymerizable with the acrylic monomer. When the ratio of the acrylic monomer is less than 80% by weight, impact resistance and weatherability of a molded article is easily lowered. When hollow rubber particles obtained from a butadiene polymer are used, weatherability of a molded article is deteriorated.
Examples of the above acrylic polymer include butyl acrylate rubber, butadiene-butyl acrylate rubber, 2-ethylhexyl-acrylate-butyl acrylate rubber, 2-ethylhexyl-methacrylate-butyl acrylate rubber, dimethylsiloxane-butyl acrylate rubber, a composite rubber of silicone rubber and butyl acrylate rubber and the like.
The above acrylic polymer has a glass transition temperature (Tg) of at most 0xc2x0 C., preferably xe2x88x9220xc2x0 to xe2x88x9240xc2x0 C. from the viewpoint of impact resistance.
Further, the average void ratio of the above hollow rubber particles in a latex state is 3 to 90% by volume, preferably 10 to 60% by volume, more preferably 40 to 60% by volume. When the average void ratio is less than 3% by volume, improving effect on impact resistance is not sufficiently imparted. On the other hand, when the ratio is more than 90% by volume, hollow rubber particles may break at molding and impact strength cannot be improved stably.
The average void ratio of the above hollow rubber particles can be measured by the following method.
That is, the average void ratio can be measured by staining the particles with ruthenium tetraoxide and observing the same according to TEM after hollow rubber particles present in a latex state are embedded with an epoxy resin or the like. Alternatively, the average void ratio can be calculated by accurately measuring each diameter of rubber particles in the latex using microtrack UPA or the like and then measuring light scattering strength of the same rubber latex.
The average particle diameter of the hollow rubber particles is generally 0.03 to 2.0 xcexcm, preferably 0.03 to 0.5 xcexcm, more preferably 0.05 to 0.3 xcexcm from the viewpoint of improvement on impact strength and polymerization stability of hollow rubber particles.
The hollow rubber particles may be formed of a single layer or at least two layers. It is preferable that hollow rubber particles are prepared by forming a seed and then grafting the seed with a monomer copolymerizable therewith from the viewpoint that polymerization of rubber particles is stable and uniform rubber particles can be obtained.
As the graft monomer component to be grafted with the above hollow rubber particles, there is used a component comprising 50 to 100% by weight, preferably 60 to 100% by weight of methyl methacrylate, 0 to 50% by weight, preferably 0 to 40% by weight of alkyl methacrylate having 2 to 8 carbon atoms in the alkyl group and/or alkyl acrylate having 1 to 8 carbon atoms in the alkyl group and 0 to 25% by weight of acrylonitrile from the viewpoint of processibility and compatibility with a chlorinated vinyl chloride resin. Examples of the preferable graft monomer component include a component comprising 60 to 100% by weight of methyl methacrylate and 0 to 40% by weight of alkyl methacrylate having 2 to 8 carbon atoms in the alkyl group and/or alkyl acrylate having 1 to 8 carbon atoms in the alkyl group. Particularly preferable is a component comprising 100% by weight of methyl methacrylate.
The graft ratio of the graft monomer component to the above hollow rubber particles is 30 to 90% by weight, preferably 70 to 90% by weight of hollow rubber particles in the acrylic graft rubber copolymer from the viewpoint of impact resistance.
The average particle diameter of the above acrylic graft rubber copolymer is usually 0.033 to 2.2 xcexcm, preferably 0.033 to 0.55 xcexcm, more preferably 0.055 to 0.33 xcexcm.
As a method of preparing the above acrylic graft rubber copolymer, various methods are known. For example, the copolymer can be prepared by a method described in WO 00/02963 pamphlet.
The amount of the above acrylic graft rubber copolymer is 3 to 20 parts by weight, preferably 4 to 12 parts by weight based on 100 parts by weight of a chlorinated vinyl chloride resin. When the amount is less than 3 parts by weight, impact resistance is not sufficiently improved. When the amount is more than 20 parts by weight, heat resistance, an original property in case of using a chlorinated vinyl chloride resin as a base resin, becomes insufficient.
In order to improve heat stability at extrusion processing, a stabilizer, a lubricant and a dark-color pigment may be added to the chlorinated vinyl chloride resin composition of the present invention comprising a chlorinated vinyl chloride resin and an acrylic graft rubber copolymer.
As the above stabilizer, a tin stabilizer is preferable from the viewpoint of improvement on heat stability and low toxicity.
Examples of the tin stabilizer include alkyltin such as methyltin, butyltin or octyltin, dialkyltin dicarboxylate such as butyltin propionate, alkyltin mercaptide such as methyltin mercaptide, butyltin mercaptide or octyltin mercaptide, alkyltin maleate ester such as butyltin maleate ester or octyltin maleate ester, alkyltin maleate polymer such as butyltin maleate polymer or octyltin maleate polymer, alkyltin mercaptocarboxylate such as butyltin mercaptopropionate, dialkyltin bis(alkylmercaptocarboxylate), and di-n-octyltin-S,Sxe2x80x2-bis(isooctylmercaptoacetate). These may be used alone or in combination of two or more. However, it is preferable to use at least two kinds of tin stabilizers selected from the above in combination since extremely excellent heat stability effects can be obtained and problems of coloration and generation of burn mark at extrusion molding are greatly prevented.
When at least two kinds of tin stabilizers selected from the above tin stabilizers are used in combination, specific examples of the combination include a combination of 3 parts by weight of alkyltin mercaptide such as butyltin mercaptide and 0.3 to 0.7 part by weight of alkyltin mercaptocarboxylate such as butyltin mercaptopropionate, and a combination of 3 parts by weight of alkyltin mercaptide such as octyltin mercaptide and 0.3 to 0.7 part by weight of alkyltin maleate ester such as butyltin maleate ester.
The amount of the above tin stabilizer is preferably 1 to 5 parts by weight based on 100 parts by weight of a chlorinated vinyl chloride resin. In order to improve heat stability of the chlorinated vinyl chloride resin, the amount of the tin stabilizer is preferably at least 1 part by weight. However, when the amount is more than 5 parts by weight, heat stability effect reaches a state of saturation.
As the lubricant, at least one kind of generally used lubricants, for example, di- or trioleate of polyglycerol, polyethylene wax, oxidized polyethylene and high molecular paraffin wax can be used without particular limitation. A preferable lubricant is polyethylene wax from the viewpoint of higher lubricating property.
As to the polyethylene wax, it is preferable to use oxidation-type modified polyethylene wax having an acid number of 0.1 to 10 mg/g measured by JIS K5902. When the acid number is adjusted to at least 0.1 mg/g, compatibility with the chlorinated vinyl chloride resin is improved and then desirable products can be obtained by kneading. In addition, when the acid number is adjusted to at most 10 mg/g, sliding of a chlorinated vinyl chloride resin through the metal face of a mold is improved, molded articles becomes glossy and burn mark is not formed. In addition, use of such oxidation-type modified polyethylene wax improves impact strength of a molded article. A preferable acid number is 0.5 to 5 mg/g.
The amount of the above lubricant is preferably 1.5 to 4 parts by weight based on 100 parts by weight of a chlorinated vinyl chloride resin. In order to decrease melt viscosity to improve extrusion processibility, the amount of the lubricant is preferably at least 1.5 parts by weight. In order to avoid pulsation caused by resin discharge at extrusion processing, the amount of the lubricant is preferably at most 4 parts by weight.
As the above dark-color pigment, pigments conventionally used can be employed.
It is preferable that the amount of the above dark-color pigment is 0.01 to 1 part based on 100 parts by weight of a chlorinated vinyl chloride resin.
Even when a dark-color pigment is added to the chlorinated vinyl chloride resin composition of the present invention, processibility, heat resistance and impact resistance are not deteriorated. Therefore, there can be obtained a dark-color siding molded article which was impossible to obtain according to prior arts.
To the chlorinated vinyl chloride resin composition of the present invention mentioned above may be added a filler such as titanium dioxide or calcium carbonate, an appropriate processibility improving agent and a coloring agent such as a non-dark-color pigment which are usually used in extrusion processing of a chlorinated vinyl chloride resin, in addition to the above components.
The chlorinated vinyl chloride resin composition of the present invention can be molded by conventional siding extrusion. For example, the composition and other resin compositions are coextruded at the same time using a conventional twin-screw extruder, and any embossing roll, draw-off roll or former may be used to obtain a desired siding molded article, for example, a housing siding sheet having or not having a dark color.
In this way, it is possible to obtain a siding molded article having Gardner strength of at least 0.68 mxc2x7kg/mm (1.5 inchxc2x7lbs/mil) at 23xc2x0 C. and HDT of at least 87.7xc2x0 C. (190xc2x0 F.), which was impossible to obtain according to prior arts.